The present invention relates to an improved wellhead structure which is particularly adapted to subsea wells. Such structure includes a wellhead housing and an improved hanger and seal assembly which can be landed and set in a single trip.
Prior to the present invention many efforts have been made to provide a satisfactory hanger and seal assembly which allows the landing of the hanger, cementing and the setting of the seal in the annulus between the exterior of the hanger and the interior of the housing.
The R. W. Walker U.S. Pat. No. 3,273,646 discloses a hanger and seal assembly in which a snap ring is used to engage within a groove within the interior of the housing and the seal is run in the annulus above a port which allows the circulation of cement to proceed before the seal is set responsive to rotation of the setting sleeve to force the seal downward below the port and to land on a shoulder against which it is compressed axially to cause it to expand radially and seal across the annulus.
The B. H. Nelson et al U.S. Pat. No. 3,404,736 discloses an annulus seal in which the seal is positioned within the annulus and held in the unset position by a shear pin. The rotation of the setting sleeve causes the pin to shear and the seal and wedge ring to move downward to set the holddown ring and to compress the resilient seal into sealing engagement with the walls of the annulus.
The J. H. Hynes et al U.S. Pat. No. 3,797,864 discloses another annulus seal which is set by rotation to compress the seal axially. This seal assembly includes end rings with marginal lips which engage the end of the elastomeric seal and when the seal is compressed the lips are deformed into metal-to-metal sealing engagement with the walls of the annulus. The Slyker et al U.S. Pat. No. 4,521,040 discloses a modification of the Hynes et al structure.
Another hanger seal which is set by threading a nut on external threads of the hanger includes a seal body having a plurality of outer metal fins extending outwardly and downwardly and having elastomeric material between the fins, a plurality of inner metal fins extending radially inward and having elastomeric material between the fins and a connection between the seal body and a lower body having an upstanding rim which when the bodies are forced together sets the outer seal legs. Another hanger nut thread set seal includes both inner and outer seal legs which diverge and are loaded by inner and outer rims on the upper body and lower body to set all four seal legs into sealing engagement with the walls of the housing-hanger annulus.
Other prior patents have utilized metal end caps for an elastomeric annulus so that on setting of the seal by compression, the lips of the end caps engage the walls of the annulus to both seal and also protect against the extrusion of the elastomeric material. An example of such structure can be seen in the U.S. Pat. No. 4,496,162 to McEver et al (movement of the seal ring onto enlarged diameter portion of hanger sets the seal ring into sealed position).
The B.F. Baugh U.S. Pat. No. 4,615,544 discloses another type of annulus seal which is set by rotation of a setting sleeve. The seal includes a Z-shaped portion having a plurality of frustoconical metal rings positively connected by links and the grooves formed by the rings being filled with resilient elastomeric members. The seal is set by axial compression which forces the inner and outer ends of the rings and the resilient members into sealing engagement with the walls of the annulus to be sealed.
U.S. Pat. No. 4,572,515 to A. J. Grazoli discloses a seal for sealing between the walls of a seat ring and body in a ball valve. The seal is a ring of polytetrafluoroethylene which includes spaced apart, outwardly diverging sealing lips for sealing against the wall of the body and outwardly diverging sealing lips for sealing against the wall of the seat ring.
Another prior structure is shown in U.S. Pat. No. 4,823,871 wherein the seal assembly included outer lips flaring outwardly from the seal body and having a resilient member between such lips and inner lips which flare inwardly and towards each other with a resilient member between such inner lips. The seal assembly includes structure which exerts a force on at least one of the outer lips to urge it outwardly about its base connection of the seal body into tight sealing engagement with the interior of the housing. The inner lips have a free diameter which is less than the outer sealing surface of the hanger against which they are to seal and thus the movement of these inner lips onto the hanger sealing surface brings them into sealing engagement with the hanger sealing surface.